You quote John 18: but what does that have to do with your point? Jesus said His kingdom was not of this world.
36 Jesus replied, “My kingdom is not from this world. If my kingdom were from this world, my servants would be fighting to keep me from being handed over to the Jewish authorities. But as it is, my kingdom is not from here.” 37 Then Pilate said, “So you are a king!” Jesus replied, “You say that I am a king. For this reason I was born, and for this reason I came into the world – to testify to the truth. Everyone who belongs to the truth listens to my voice.” 38 Pilate asked, “What is truth?”
Obviously, Pilot did not get what world Jesus was talking about or what his unique truth was was testifying about. Jesus was not the truth, but one sent to testify to the truth. Apparently many listened to His voice, but none tried to save Him. None thought he was himself the Truth. None believed in His resurrection before it happened. So, exactly who were there with Jesus who "belongs to the truth." Thus who believed what to Jesus said." Today there are at least 45,000 different Christian denominations all claiming to have listened to Jesus but come up with conflicting theologies. Which is hearing His voice?
In your John 8 citation Jesus specifically says He knows God. He come from God and obeys God's teachings. The only teachings from God at that point was compliance with the Jewish law.
Then they said to Jesus, “We were not born as a result of immorality! We have only one Father, God himself.” 42Jesus replied, “If God were your Father, you would love me, for I have come from God and am now here. I have not come on my own initiative, but he sent me. 43Why don’t you understand what I am saying? It is because you cannot accept my teaching. 44You people are from your father the devil, and you want to do what your father desires. He was a murderer from the beginning, and does not uphold the truth, because there is no truth in him. Whenever he lies, he speaks according to his own nature, because he is a liar and the father of lies. 45But because I am telling you the truth, you do not believe me. 46Who among you can prove me guilty of any sin? If I am telling you the truth, why don’t you believe me? 47The one who belongs to God listens and responds to God’s words. You don’t listen and respond, because you don’t belong to God.”
48 The Judeans replied, “Aren’t we correct in saying that you are a Samaritan and are possessed by a demon?” 49 Jesus answered, “I am not possessed by a demon, but I honor my Father – and yet you dishonor me. 50 I am not trying to get praise for myself. There is one who demands it, and he also judges. 51 I tell you the solemn truth, if anyone obeys my teaching, he will never see death.”
52 Then the Judeans responded, “Now we know you’re possessed by a demon! Both Abraham and the prophets died, and yet you say, ‘If anyone obeys my teaching, he will never experience death.’ 53 You aren’t greater than our father Abraham who died, are you? And the prophets died too! Who do you claim to be?” 54 Jesus replied, “If I glorify myself, my glory is worthless. The one who glorifies me is my Father, about whom you people say, ‘He is our God.’ 55 Yet you do not know him, but I know him. If I were to say that I do not know him, I would be a liar like you. But I do know him, and I obey his teaching. 56 Your father Abraham was overjoyed to see my day, and he saw it and was glad.”